Maybe I'm lucky but I've nothing but success w/Spotone dyes. Maybe I've found the right color mix. But even when I point out fairly large areas I've spotted like 4 mm X 4 mm people still don't notice. For Ilford MG IV fiber paper slightly toned in Kodak Selenium I use 9 drops of the neutral black to 1 drop of the blue black. I then let it totally dry in a small artist palette and with a slightly wet brush (depending on how dark I want to go) gradually build up the density as I draw from the dried dye.

I have had good results from the brown, sepia, black and blue black so far, but the Olive. I jest not. Olive plus water goes blue, which becomes most apparrent only after applied to the print. Yes, there is olive there with a cold blue underpinning it.

I have had a lot of sucess with spot-tone, match the colour to the paper you are using.. a little secret I like is using a very good brush, Most people I see spotting use a nose-hair size tip, I use a windsor newton series 7 finest sable brush #2, it has a larger brush but in actual case you are only using the point of the brush to ****drop**** a slight tone into the area you are working on. As well this brush allows you to gather an larger amount of dye to continually drop in a defined pattern into the spot.
I find the trick is to camoflage the area and work with adjacent densitys to hide the spot.
In colour look closely at the grain of the print with a loupe, you will find it is a series of colours. Isolate those colours on your pallette and drop them randomly into the dust mark and slowly build up the density.
Put on some good music and enjoy yourself because no-one else will clean up these dust mites, so you should get good at it. I am suprised at how many technicans I meet , do not know how to spot well.
Also a very important point, I just turned 50 and my eyesight at close distances was getting shaky to say the least. Go to a local drugstore and get those simple reading glasses, it made a world of difference for me. Now I drop the dyes with pinpoint accuraccy rather than a random bombing pattern.

Spotting is no big deal to me. I use Spotone and, mostly, warmtone papers with some Ilford MG IV neutral tone. I usually tone in Kodak Rapid Selenium Toner, Nelson Gold Toner or Kodak Brown Toner. I have a plastic "I Can't Believe It's Not Butter" canister top that has been splashed with Brown, Sepia and #3. Although it dries out, it can be reused until nothing is left. I use it following every print session and I can mix the colors to match virtually perfectly. I give a #000 sable brush a lick with my tongue and dip it into the solidified mixture, wipe the brush to remove the excess and go to work.

The trick is to start light and work darker and to use the smallest amout of Spotone possible.

By the way, a bottle of Spotone lasts for years. I used my first Spotone #3 bottle for 20 years before it needed to be replaced. I splashed my current mixture on the canister top over four years ago and I'm still using it. It's no wonder the company recently went out of business.

I don't have any experience with the pens but have used a Spotone process for... well, forever. I use a favorite 15/0 brush (15 0's rather than a 000 or 0 or whatever). I've had this particular brush almost from the beginning of my spotting life, yet to find another 15/0, 000, 00, 0 or whatever quite as good. Anyway, the Spotone is mixed on a small tile as per the paper type it is to match and let dry (for a paper new to ones usage it may take several attempts at different mixes to get an acceptable match, but the documentation that comes with the Spotone is a good starting point). One mix will last me months. When spotting, I just add enough moisture to the brush in order make the dried Spotone mix liquid again and then only enough Spotone to make the right density for the area to be spotted. I put the brush in my mouth for just a very little bit of moisture as dipping it in a water source tends to be too much liquid for my technique [and please don't tell me what this will or has done to me, I’m not sure I want to know])... Keeping scraps of fully processed paper of the type to be spotted (processed in the same chemicals and toned the same way). these are used when spotting to insure the correct density mix for the print (placing the scrap next to the area to be spotted). I dab the Spotone on rather than using brush like strokes, like trying to make tiny dots until the area is ‘spotted’.

Spotting is no big deal to me. I use Spotone and, mostly, warmtone papers with some Ilford MG IV neutral tone. I usually tone in Kodak Rapid Selenium Toner, Nelson Gold Toner or Kodak Brown Toner. I have a plastic "I Can't Believe It's Not Butter" canister top that has been splashed with Brown, Sepia and #3. Although it dries out, it can be reused until nothing is left. I use it following every print session and I can mix the colors to match virtually perfectly. I give a #000 sable brush a lick with my tongue and dip it into the solidified mixture, wipe the brush to remove the excess and go to work.

The trick is to start light and work darker and to use the smallest amout of Spotone possible.

By the way, a bottle of Spotone lasts for years. I used my first Spotone #3 bottle for 20 years before it needed to be replaced. I splashed my current mixture on the canister top over four years ago and I'm still using it. It's no wonder the company recently went out of business.

Same method I use. I can't focus close enough with my current contacts, so I went to Hobby Lobby and got a magnifying visor and the max magnification lens. I think ideally, it would be best to use one of those work lamps with the circular florescent bulb and the highest power magnifying lens in the middle as possible.

Additionally, I've had best luck with a 10/0 brush. I've got a saucer into which I've dropped three or four drops of spotone #3 and let it dry. I've been using that saucer for about a month and I'm not out of spotone yet. To apply the dye to the print, I lightly drag the very end of the very tip bristles of the brush (at the point where I can barely see it with a magnifier) across the spot and slowly build up to just under the density I want.

I have used Spotone for a long time, I handle it just like water colors. I put a few drops of each color (1,2,3.) on a white pallette glass/plastic/ceramic,
and let it dry. Using a 0000 or smaller Kolenski Sable brush slightly moisened
with water and photoflo ( a drop of dish washing detergent works just fine)
mix the color necessary to match the spot and apply it. Color dye applied to the same kind of pallet works very well also. Done properly you cannot see the applied dye on the print surface. BTW I hate spotting even though it is very easy and quick to do. Sounds like we all are using basically the same
methods.